The British Geological Survey recorded a Magnitude 1.3 Earthquake at a depth of 2 km, about 4 km to the west of Falmouth in Cornwall, at about 10.45 pm British Summertime (about 9.45 pm GMT), on Tuesday 2 July 2012. There are no reports of any injuries or damage (unsurprising for a quake this small), but the tremor was felt in Falmouth and nearby Penryn.
The location of the 2 July 2013 Falmouth Earthquake. Google Maps.
The precise cause of Earthquakes around the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.
Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process.
Glacial rebound seems an unlikely cause of Earthquakes in the south of Cornwall, an area that was never glaciated, but this is not entirely the case. The northwest of Scotland is rising up faster than any other part of the UK, but the Earth's crust onland in the UK is fairly thick, and does not bend particularly freely, whereas the crust beneath the Channel is comparatively thin and more inclined to bend under stress. Thus uplift in Scotland can cause the entire landmass of Great Britain to pivot, causing movement in the rocks beneath the Channel, and affecting the south coast area.
Witness accounts can help scientists to understand Earthquakes and the geological processes that cause them. If you felt this quake (or if you were in the area and did not, which is also useful information) then you can report it to the British Geological Survey here.
See also Earthquake off the coast of Cornwall, Earthquake in east Cornwall, Earthquake in Somerset, Earthquake in Herefordshire and Earthquake in West Sussex, England.
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